Actin polymerization inhibition by targeting ARPC2 affects intestinal stem cell homeostasis.

Background: The rapid turnover of the intestinal epithelium is driven by the proliferation and differentiation of intestinal stem cells (ISCs). The dynamics of the F-actin cytoskeleton are critical for maintaining intercellular force and the signal transduction network. However, it remains unclear how direct interference with actin polymerization impacts ISC homeostasis. This study aims to reveal the regulatory effects of the F-actin cytoskeleton on the homeostasis of intestinal epithelium, as well as the potential risks of benproperine (BPP) as an anti-tumor drug. Methods: Phalloidin fluorescence staining was utilized to test F-actin polymerization. Flow cytometry and IHC staining were employed to discriminate different types of intestinal epithelial cells. Cell proliferation was assessed through bromo-deoxyuridine (BrdU) and 5-ethynyl-2'-deoxyuridine (EdU) incorporation assays. The proliferation and differentiation of intestinal stem cells were replicated in vitro through organoid culture. Epithelial migration was evaluated through BrdU pulse labeling and chasing in mice. Results: The F-actin content was observed to significantly increase as crypt cells migrated into the villus region. Additionally, actin polymerization in secretory cells, especially in Paneth cells (PCs), was much higher than that in neighboring ISCs. Treatment with the newly identified actin-related protein 2/3 complex subunit 2 (ARPC2) inhibitor BPP led to a dose-dependent increase or inhibition of intestinal organoid growth in vitro and crypt cell proliferation in vivo. Compared with the vehicle group, BPP treatment decreased the expression of Lgr5 ISC feature genes in vivo and in organoid culture. Meanwhile, PC differentiation derived from ISCs and progenitors was decreased by inhibition of F-actin polymerization. Mechanistically, BPP-induced actin polymerization inhibition may activate the Yes1-associated transcriptional regulator pathway, which affects ISC proliferation and differentiation. Accordingly, BPP treatment affected intestinal epithelial cell migration in a dose-dependent manner. Conclusion: Our findings indicate that the regulation of cytoskeleton reorganization can affect ISC homeostasis. In addition, inhibiting ARPC2 with the Food and Drug Administration-approved drug BPP represents a novel approach to influencing the turnover of intestinal epithelial cells.

A crosslinking strategy to make neutral polysaccharide nanofibers robust and biocompatible: With konjac glucomannan as an example.

Neutral polysaccharides such as konjac glucomannan, starch and pullulan are abundant in nature and have unique property. Their nanofibers hold great potential for biomedicine, which however, are seldom applied in the field due to the lack of crosslinking method. In this work, we report a periodate oxidation - adipic acid dihydrazide (ADH) crosslinking strategy to prepare robust and biocompatible neutral polysaccharide nanofibers. Neutral polysaccharides with adjacent dihydroxyl groups are firstly partially oxidized with periodate to give dialdehyde polysaccharides, and their electrospun nanofibers are then crosslinked with ADH to form dihydrazone crosslinkers. The resulting crosslinked neutral polysaccharide nanofibers exhibit high water resistance and excellent mechanical properties because of the high reactivity of Schiff base crosslinking reaction. Moreover, the crosslinked neutral polysaccharide nanofibers show good biocompatibility due to the low toxicity of ADH. These robust and biocompatible neutral polysaccharide nanofibers are expected to seek extensive applications in a variety of biomedical fields.

A novel morphometry system automatically assessing the growth and regeneration of intestinal organoids.

As compared with 2D cell line cultures, 3D intestinal organoids are better at maximally recapitulating the physiological features of stem cells in vivo. However, the complex 3D structure is an obstacle which must be objectively and automatically evaluated to assess colony growth and regeneration. Meanwhile, no internal standard currently exists for evaluating the size of heterogeneities in organoids or defining those regenerating colonies. Herein, we developed a simple morphometry system to image MTT-stained organoids. The growth curve of organoids can be automatically generated based upon analyzing the integrated optical density using software. Referencing the definition standards of in vivo regenerating crypts, the perimeters of crypts cultured 24 h after seeding were selected as an "Organoid Unit" to further evaluate colony survival rate and colony size heterogeneities after exposure to varying doses of irradiation. Moreover, the morphometry-based quantification data collected confirmed other findings associated with radiation sensitizing effects of ataxia telangiectasia mutated (ATM) and ataxia telangiectasia and Rad3-related protein (ATR) inhibitor and the radiation protective effect of IL-22. In summary, the novel organoid morphometry system combined with a new internal reference is a practical means for standardizing assessment of growth, survival and regeneration of intestinal organoid colonies. This method has promise to facilitate drug screens in intestinal and other organoid systems.

Identification of G2/M phase transition by sequential nuclear and cytoplasmic changes and molecular markers in mice intestinal epithelial cells.

Although the regulatory network of G2/M phase transition has been intensively studied in mammalian cell lines, the identification of morphological and molecular markers to identify G2/M phase transition in vivo remains elusive. In this study, we found no obvious morphological changes between the S phase and G2 phase in mice intestinal epithelial cells. The G2 phase could be identified by Brdu incorporation resistance, marginal and scattered foci of histone H3 phosphorylated at Ser10 (pHH3), and relatively intact Golgi ribbon. Prophase starts with nuclear transformation in situ, which was identified by a series of prophase markers including nuclear translocation of cyclinB1, fragmentation of the Golgi complex, and a significant increase in pHH3. The nucleus started to move upwards in the late prophase and finally rounded up at the apical surface. Then, metaphase was initiated as the level of pHH3 peaked. During anaphase and telophase, pHH3 sharply decreased, while Ki67 was obviously bound to chromosomes, and PCNA was distributed throughout the whole cell. Based on the aforementioned markers and Brdu pulse labeling, it was estimated to take about one hour for most crypt cells to go through the G2 phase and about two hours to go through the G2-M phase. It took much longer for crypt base columnar (CBC) stem cells to undergo G2-prophase than rapid transit amplifying cells. In summary, a series of sequentially presenting markers could be used to indicate the progress of G2/M events in intestinal epithelial cells and other epithelial systems in vivo.

Effects of pectin structure and crosslinking method on the properties of crosslinked pectin nanofibers.

We reported crosslinking of electrospun nanofibers of three representative pectins (high-methoxylated, low-methoxylated, low-methoxylated and amidated pectin) and characterization of the crosslinked nanofibers. One mono-crosslinking strategy and two dual-crosslinking strategies were developed. Mono-crosslinking is achieved using calcium ions (Ca2+) to crosslink carboxylate ions in galacturonic acid residues. Dual-crosslinking is achieved using covalent crosslinking reagents glutaraldehyde (GLU) or adipic acid dihydrazide (ADH) to further crosslink hydroxyl groups or carboxylate ions after Ca2+ crosslinking. Mechanical tests and degradation experiments indicated pectin structure affected mechanical and degradation properties of Ca2+-crosslinked nanofibers remarkably. Subsequent GLU crosslinking improved their mechanical strength moderately but did not inhibit their degradation, while subsequent ADH crosslinking improved their mechanical strength and slowed down their degradation dramatically. Cell studies demonstrated that most crosslinked pectin nanofibers were of no obvious cytotoxicity, and both ADH crosslinking and high degree of methoxylation facilitated cell adhesion and proliferation on pectin nanofiber mats.